The present invention relates to a fuel pump assembly for a motor vehicle that can be connected upstream from a fuel pump of the motor vehicle in a fuel line of the motor vehicle, having a pump housing and a pump device situated thereon with which fuel can be pumped into and/or through the pump housing when the pump device is in its active state, the pump device having at least one stroke piston pump having an inlet valve and an outlet valve that are alternately opened and closed by pressure actuation when the pump device is active.
From utility patent DE 89 09 261 U1, a corresponding fuel pump assembly is known with which, for example before the first operation of the internal combustion engine of the motor vehicle or before the commissioning of the internal combustion engine after complete emptying of the fuel tank of the motor vehicle, the fuel line between the fuel tank and the internal combustion engine can be evacuated of air and at the same time filled with fuel. The fuel pump assembly is integrated into a filter device that can be connected upstream from a fuel pump of the motor vehicle, for filtering the fuel that is taken from the fuel tank and that can be supplied to the fuel pump; the filtered fuel can be supplied by the fuel pump to the injection valves or to the injection pump of the internal combustion engine. Thus, the pump housing of the fuel pump assembly is at the same time a part of the filter device.
On the pump housing there is situated a pump device that has a stroke piston pump. The stroke piston pump includes an inlet valve having a ball-shaped valve body and an outlet valve whose valve body is formed by the piston of the stroke piston pump. By means of the pump device, the fuel can be pumped into and/or through the pump housing when the pump device is in its active state, the inlet valve and the outlet valve being alternately opened and closed by pressure actuation when the pump device is active. In order to transfer the pump device from its inactive state to its active state, the actuating element of the stroke piston pump, fashioned as a knurled wheel, must be unscrewed from the cover of the housing of the filter device. If, on the other hand, the actuating element is screwed to the housing cover, the pump device is in its inactive state, in which the pump device holds the outlet valve in its open position. When the pump device is inactive, the inlet valve is closed, because the ball-shaped valve body of the inlet valve is pressed against the valve seat due to the force of the weight acting on the valve body and due to a ramp declining in the direction of the valve seat of the inlet valve.
Here, it is disadvantageous that when the pump device is inactive, the fuel pumped through the fuel pump assembly by the fuel pump of the motor vehicle has to lift the ball-shaped valve body of the inlet valve from its valve seat. This results in a loss of pressure in the fuel stream conveyed by the fuel pump that either has to be accepted, which is associated with a worsening of the supply of fuel to the internal combustion engine and thus of the performance of the internal combustion engine, or else compensated by the use of a more powerful fuel pump. Both procedures are associated with an increased consumption of fuel, which is unacceptable in particular with regard to today's requirements of energy efficiency of internal combustion engines, or motor vehicles equipped therewith.